This invention relates to an electromagnetic fuel injector for use in an electronically controlled fuel injection system of a single- or multiple-point type for an internal combustion engine in an automotive vehicle.
FIG. 1 shows a vertical sectional view of a conventional electromagnetic fuel injector designated by reference numeral 1. The electromagnetic fuel injector 1 is provided with a fuel injection nozzel 3 at its front end. A valve housing 2 is provided with a fuel passage 4 extending along its axis, and a plunger-like valve body 5 is inserted into the fuel passage 4. An armature 6 is fixed to the rear end of the valve body 5. The valve housing 2 is retained by an electromagnetic housing 7 at its front portion. A fixed magnet core 8 and an exciting coil or winding 9 are accomodated in the electromagnetic housing 7 at its rear portion. In response to the control signal inputted from a terminal 10 to the exciting coil 9, the valve body 5 is effective to axially reciprocate for discharging pressurized liquid fuel from the fuel injection nozzle 3. FIG. 2 shows an enlarged sectional view of the fuel injection nozzle 3 in FIG. 1. As may be seen, the inner surface of the nozzle 3 serves as a valve seat 3a which is adapted to come into contact with a valve member 5a of the valve body 5. The cylindrical inner surface of the fuel passage 4 serves to guide a slide portion of the valve body 5. The front portion of the valve housing 2 is protected by a cover 7a and the rear portion thereof is fixed to the front portion of the electromagnetic housing 7 with an O-ring seal 11 and a spacer 12 interposed. The valve member 5a is provided with a pintle 19 at its front end, and the pintle 19 is formed with a conical tip 19a at its front end. The outer circumference of the valve body 5 is formed with a flange 5b on the front side of the spacer 12, and the flange 5b is adapted to come into contact with the front surface of the spacer 12 when the valve body 5 moves up to the rearmost position. The electromagnetic housing 7 as a yoke is formed of a ferromagnetic material, and the exciting coil 9 is housed in a space between the electromagnetic housing 7 and the fixed magnet core 8 with O-ring seals 13 and 14 interposed. The fixed magnet core 8 is also formed of a ferromagnetic material and is provided with an axial through-hole as a fuel passage 15. A compression spring 16 is inserted into the front portion of the axial through-hole so as to normally bias against the rear end of the armature 6 and hold the valve body 5 in a closed position. The compression spring 16 abuts against the front end of a sleeve 17 which is carried in the axial through-hole of the fixed magnet core 8. A fuel filter 18 is provided at the rear end of the fuel passage 15.
In such an electromagnetic fuel injector 1, it is necessary for the valve body 5 to smoothly reciprocate and to seal the pressurized fuel with the valve member tightly contacted to the valve seat 3a in its closed position. For this purpose, it is required to fabricate the front and the rear slide portions of the valve body 5 and the guide hole 4 with a high degree of accuracy. Accordingly, the valve seat 3a and the valve member 5a are required to have a strictly limited surface roughness, roundness and axial concentricity thereof. The foremost end of the valve body 5 including the pintle 19 and its contical tip 19a needs to be formed in complicated shape so as to atomize the liquid fuel supplied to the fuel injection nozzle 3. Furthermore, the guide hole 4 and the valve body 5 are formed of stainless steel, thus rendering the fabrication of such elements more difficult and more costly.
Since the total weight of the valve body 5 and the armature 6 is relatively large, say about 5 grams, the response of the valve body 5 to the on-off operation of the exciting coil 9 is not satisfactory and the valve body 5 is likely to wear because of large impact force. For purposes of stabilization of idle engine speed and reduction in fuel consumption, it is necessary to shorten the time required for the valve body 5 to be stabilized when the valve is opened or closed.
To this end, the mass of the valve body 5 and the armature 6 may be reduced, but the diameter of the valve body 5 may not be so reduced in order that a high degree of accuracy of the slide portion he retained. To prevent a large inclination of the axis of the valve body 5 relative to the axis of the guide hole 4, the axial length of the valve body 5 may not be so shortened. Because of the above-mentioned problem, it has been considered to be difficult to establish an electromagnetic fuel injector wherein its valve body is quick in response and has good wear-resistance.
To solve such a problem, the prior art has proposed a valve structure of an electromagnetic fuel injector wherein either a valve seat or a valve member has a spherical surface, so as to allow machining accuracy of valve elements to be reduced and to greatly improve fuel injection performance and durability of a fuel injection valve with a simple structure of the valve elements and with a remarkably reduced productive cost.